Aircraft probe for measuring total temperature and pressure

ABSTRACT

A probe for an aircraft, making it possible in particular to measure the total temperature of the air flow surrounding the aircraft. The probe includes a moving vane configured to orientate itself in the axis of an air flow surrounding the moving vane and, fixed to the moving vane, a device for measuring the total temperature of the air flow.

The subject of the invention is a probe for an aircraft, making itpossible in particular to measure the total temperature of the air flowsurrounding the aircraft.

Measuring the total temperature is useful for determining the actualspeed of the aircraft. What happens is that other sensors belonging tothe aircraft are able to measure the total pressure Pt and the staticpressure Ps of the aircraft. Knowledge of these two pressures Pt and Psmake it possible to determine the Mach number M of the aircraft, usingthe following formula: $\begin{matrix}{M = \sqrt{5\left\lbrack {\left( \frac{P\quad t}{P\quad s} \right)^{2/7} - 1} \right\rbrack}} & (1)\end{matrix}$

Incidentally, the Mach number M represents the ratio between the actualspeed of the aircraft and the speed of sound. Now, the speed of sound,Vs, depends on the temperature, Ts, of the air surrounding the aircraft.

Vs={square root over (γ·r·Ts)}  (2)

where γ is a constant close to 1.4

r is the perfect gas constant

Ts is the static temperature of the air,

expressed in Kelvin.

The static temperature Ts is the temperature of the air at zero speed.This temperature is very difficult to measure on board an aircraft. Itwould be necessary to place a temperature sensor placed at the bottom ofa hole more or less perpendicular to the skin of the aircraft in aregion where the skin is more or less parallel to the air flow. Thistemperature sensor would in particular be disrupted by the skintemperature which would carry the risk of affecting the statictemperature measurement. It is therefore preferable to measure the totaltemperature Tt of the air flow by placing the temperature sensor in theair flow. The static temperature Ts can then be determined usingequation (3)

Tt=(1+0.2 M ²)Ts  (3)

All this makes it possible to determine the actual speed of the aircraftas a function of the total temperature Tt, the total pressure Pt and thestatic pressure Ps of the air flow surrounding the aircraft.

Total temperature measurement probes fixed to the skin of the aircraftare known. These probes plan for part of the air flow surrounding theaircraft to sweep over a temperature sensor. When the angle of incidenceof the aircraft with respect to the air flow surrounding it is changed,the proportion of the air flow that sweeps over the temperature sensoris disrupted and this affects the total temperature measurement Tt. Allthis becomes increasingly important since it is when the aircraft is ata high angle of incidence that its speed needs to be known withprecision.

The object of the invention is to improve the precision with which thetotal temperature Tt can be measured particularly when the angle ofincidence of the aircraft with respect to the air flow surrounding it ishigh.

To achieve this objective, the subject of the invention is a probe foran aircraft, characterized in that it comprises a moving vane intendedto orientate itself in the axis of an air flow surrounding the movingvane and, fixed to the moving vane, means for measuring the totaltemperature of the air flow.

In a particular embodiment of the invention, the following are groupedtogether in one and the same probe and fixed to a moving vane of theprobe:

means for measuring the total temperature of the air flow;

means for measuring the total pressure of the air flow;

means for measuring the static pressure of the air flow;

means for measuring the angle of incidence of the aircraft.

Grouping these various measurement means together makes it possible todetermine in a complete way the modulus and the direction of theaircraft velocity vector using a single probe. This grouping-togetheralso makes it possible to reduce the number of openings made in the skinof the aircraft.

The invention will be better understood and other advantages will becomeapparent from reading the description of a particular embodiment of theinvention, which embodiment is illustrated by the attached drawing inwhich:

FIG. 1 depicts a probe comprising:

means for measuring the total temperature of the air flow;

means for measuring the total pressure of the air flow;

means for measuring the static pressure of the air flow;

means for measuring the angle of incidence of the aircraft.

The probe depicted in FIG. 1 comprises a moving vane 1 able to rotateabout an axis 2. The vane 1 comprises an aerofoil 3 having a plane ofsymmetry, parallel to the plane of the figure and separating thepressure face side from the suction face side. The profile of theaerofoil 3 at right angles to its leading edge 4 is, for example, of theNACA OOZT type. In the example depicted, the leading edge 4 is more orless straight and is inclined with respect to the axis 2. It must beclearly understood that other aerofoil shapes could be used in order toimplement the invention. The vane 1 also comprises a shaft 5 of axis 2which penetrates the skin 6 of an aircraft. The shaft 5 is able to turnwith respect to the aircraft, for example by means of a rolling bearing7.

Because of the shape of the aerofoil 3, the vane 1 naturally orientatesitself in the axis of the air flow surrounding the moving vane 1. Theaxis of the flow is embodied by the arrow 8 depicted in FIG. 1.

The moving vane 1 further comprises means for measuring the totaltemperature of the air flow.

Advantageously, these means comprise two channels including a firstchannel 10 comprising an inlet orifice 11 more or less facing the airflow of axis 8 when the moving vane 1 is oriented along the axis 8 ofthe air flow. The first channel 10 also comprises an outlet orifice 12allowing air in the first channel 10 to escape in the direction of theaxis 8. Particles likely to be circulating in the first channel 10escape without coming into contact with a temperature sensor theposition of which will be described later. These particles consist, forexample, of water droplets or dust.

The second channel 13 comprising means for measuring the totaltemperature of the air flow comprises an inlet orifice 14 opening intothe first channel 10. The second channel 13 is, for example, more orless perpendicular to the first channel 10. Some of the air circulatingin the first channel 10 enters the second channel 13 via the inletorifice 14 and escapes from the second channel 13 via an outlet orifice15 which opens to the outside toward the rear of the moving vane 1.

The means for measuring the total temperature of the air flowfurthermore comprise a temperature sensor 16 situated inside the secondchannel 13. The temperature sensor 16 comprises, for example, a woundplatinum-based wire forming an electric resistor the resistance of whichvaries according to its temperature. The temperature sensor 16 is fixedin the second channel 13 in such a way as to avoid as far as possibleany transfers of heat between the structure of the second channel 13 andthe temperature sensor 16.

The two channels 10 and 13 are arranged in such a way that air from theflow of axis 8 circulates in the second channel 13 at low speed. Thisspeed needs to be very much lower than the speed of sound in the flowwhile at the same time being non-zero so as to prevent the temperaturesensor 16 from taking the temperature of the structure of the movingvane 1 and, in particular, the temperature of the structure of the twochannels 10 and 13.

What actually happens is that when the aircraft is flying at highaltitude, the temperature of the air flow may be well below zero degreesCelsius, and this leads to a risk of ice forming on the moving vane 1.The ice may in particular block these channels 10 and 13 and thusprevent any correct temperature measurement.

To avoid the formation of ice, the moving vane 1 comprises deicing meanscomprising, for example, a heating electric resistor arranged in thestructure of the vane. These deicing means heat up the moving vane 1 andtherefore the air which circulates in the two channels 10 and 13. Toprevent the heating-up of the air disrupting the temperaturemeasurement, orifices 17 for bleeding off the boundary layer of the aircirculating in the two channels 10 and 13 are provided.

Advantageously, the probe further comprises means for measuring thetotal pressure and the static pressure of the air flow and the angle ofincidence of the aircraft.

The means for measuring the total pressure comprise, for example, atotal pressure tapping Pt comprising a third channel 20 opening, likethe first channel 10, via an orifice 21 more or less facing the air flowof axis 8. This third channel 20 is better known by the name of Pitottube.

The means for measuring the static pressure Ps comprise, for example,two static pressure tappings 22 and 23, each situated on one of thefaces of the moving vane 1. In FIG. 1 only the pressure tapping 22 isvisible. The pressure tapping 23 is placed on the non-visible face ofthe moving vane 1, more or less symmetrically with the pressure tapping22 with respect to the plane of symmetry of the aerofoil 3. This planeof symmetry is parallel to the plane of FIG. 1. Each pressure tapping 22and 23 may comprise several orifices, three are depicted in FIG. 1 soas, in particular, to limit the cross section of each orifice in orderto cause less disruption to the flow of air surrounding the moving vane1 or alternatively so as to be able to measure pressure even if one ofthe orifices becomes blocked. The two static pressure tappings 22 and 23are in communication with a chamber situated inside the vane so as toaverage out the pressure between the two tappings 22 and 23.

The means for measuring the angle of incidence of the aircraft comprise,for example, two incidence pressure tappings 24 and 25 situated, as wasthe case with the static pressure tappings 22 and 23, on one of thefaces of the vane also more or less symmetrically with respect to theplane of symmetry of the aerofoil 3. The incidence pressure tappings 24and 25 are not in communication, and it is the difference between thepressures between each tapping 24 and 25 that makes it possible todetermine the exact angle of incidence of the moving vane 1 and thusthat of the aircraft. In order to improve the sensitivity of theincidence measurement, the pressure tappings 24 and 25 can be placed inthe immediate vicinity of the leading edge 4 of the moving vane 1.

The use of the information originating from the various total, staticand incidence pressure tappings is, for example, described in Frenchpatent FR 2 665 539 filed on Aug. 3, 1990 in the name of the applicantcompany.

That patent describes in particular the feedback control of the angularposition of the moving vane 1 about its axis 2 so that the aerofoil 3 ofthe moving vane 1 is best aligned with the axis 8 of the air flow. Theorientation, thus improved, of the moving vane 1 makes it possible, inparticular, to have even better control over the circulation of thestreams of air in the channels 10 and 13.

What is claimed is:
 1. A probe for an aircraft, comprising: a movingvane configured to orientate itself in an axis of an air flowsurrounding the moving vane; and means, fixed to the moving vane, formeasuring a total temperature of the air flow, wherein the means formeasuring the total temperature comprises: a first channel comprising anair inlet orifice substantially facing the air flow and an air outletorifice; a second channel having an air inlet situated in the firstchannel; and a temperature sensor fixed in the second channel.
 2. Theprobe as claimed in claim 1, wherein the second channel is substantiallyperpendicular to the first channel.
 3. The probe as claimed in claim 1,wherein the first and second channels comprise a plurality of orificesallowing a boundary layer of air flowing through the channels to be bledoff toward an outside of the probe.
 4. The probe as claimed in claim 2,wherein the first and second channels comprise a plurality of orificesallowing a boundary layer of air flowing through the channels to be bledoff toward an outside of the probe.
 5. The probe as claimed in claim 1,further comprising, fixed to the moving vane: means for measuring atotal pressure of the air flow; means for measuring a static pressure ofthe air flow; and means for measuring an angle of incidence of theaircraft.
 6. The probe as claimed in claim 1, further comprising, fixedto the moving vane: means for measuring a total pressure of the airflow; means for measuring a static pressure of the air flow; and meansfor measuring an angle of incidence of the aircraft.
 7. The probe asclaimed in claim 2, further comprising, fixed to the moving vane: meansfor measuring a total pressure of the air flow; means for measuring astatic pressure of the air flow; and means for measuring an angle ofincidence of the aircraft.
 8. The probe as claimed in claim 3, furthercomprising, fixed to the moving vane: means for measuring a totalpressure of the air flow; means for measuring a static pressure of theair flow; and means for measuring an angle of incidence of the aircraft.9. The probe as claimed in claim 4, further comprising, fixed to themoving vane: means for measuring a total pressure of the air flow; meansfor measuring a static pressure of the air flow; and means for measuringan angle of incidence of the aircraft.
 10. The probe as claimed in claim5, wherein the means for measuring the angle of incidence of theaircraft comprises two incidence pressure tappings each situated on oneof faces of the moving vane substantially symmetrically with respect toa plane of symmetry of the moving vane, and wherein an orientation ofthe moving vane with respect to a direction of the air flow is feedbackcontrolled with pressures recorded at the two incidence pressuretappings being made substantially equal.
 11. The probe as claimed inclaim 6, wherein the means for measuring the angle of incidence of theaircraft comprises two incidence pressure tappings each situated on oneof faces of the moving vane substantially symmetrically with respect toa plane of symmetry of the moving vane, and wherein an orientation ofthe moving vane with respect to a direction of the air flow is feedbackcontrolled with pressures recorded at the two incidence pressuretappings being made substantially equal.
 12. The probe as claimed inclaim 7, wherein the means for measuring the angle of incidence of theaircraft comprises two incidence pressure tappings each situated on oneof faces of the moving vane substantially symmetrically with respect toa plane of symmetry of the moving vane, and wherein an orientation ofthe moving vane with respect to a direction of the air flow is feedbackcontrolled with pressures recorded at the two incidence pressuretappings being made substantially equal.
 13. The probe as claimed inclaim 8, wherein the means for measuring the angle of incidence of theaircraft comprises two incidence pressure tappings each situated on oneof faces of the moving vane substantially symmetrically with respect toa plane of symmetry of the moving vane, and wherein an orientation ofthe moving vane with respect to a direction of the air flow is feedbackcontrolled with pressures recorded at the two incidence pressuretappings being made substantially equal.
 14. The probe as claimed inclaim 9, wherein the means for measuring the angle of incidence of theaircraft comprises two incidence pressure tappings each situated on oneof faces of the moving vane substantially symmetrically with respect toa plane of symmetry of the moving vane, and wherein an orientation ofthe moving vane with respect to a direction of the air flow is feedbackcontrolled with pressures recorded at the two incidence pressuretappings being made substantially equal.